Method for coating an article

ABSTRACT

A method for coating an article with a layer of coating material. The article is first cooled to a temperature lower than the freezing point of a chlorofluoro ethane. Then there is prepared a suspension of said chlorofluoro ethane as a suspending medium with coating particles of the coating material dispersed therein, the particles being insoluble in the chlorofluoro ethane. The suspension is kept at a temperature higher than the freezing point of chlorofluoro ethane, and the article is immersed in said suspension so as to form a frozen layer of the suspension on the surface of the article by freezing of the chlorofluoro ethane. The article is taken out of the suspension and the chlorofluoro ethane contained in the frozen layer is removed by heating the article at a temperature higher than the boiling point of the chlorofluoro ethane to leave a layer of particles on the article. The article is then further heated so that the particles remaining on the surface of the article form a layer of the coating material on the article.

United States Patent Ohkuma Oct. 21, 1975 METHOD FOR COATING AN ARTICLE3,773,579 11/1973 Michelson et al. 117/49 x [75] Inventor: AkihiroOhkuma, Hirakata, Japan Primary ExaminerHarry J. Gwinnell [73] Ass1gnee:Matsushlta Electric Industrial Co., Attorney, Agent, or pirm wenderoth,Lind & Ponack Ltd., Kadoma, Japan [21] Appl 435577 A method for coatingan article with a layer of coating material. The article is first cooledto a temperature 52 US. Cl. 427/101; 427/277; 427/299; lower than thefreezing point of a chlorofluoro ethane- 427/331; 427 375; 427 430 Thenthere is prepared a suspension of said chloro- 51 Int. 01. B05D l/18;BOSD 3/00 fluero ethane as a suspending medium with coating 58] Fi ld fSearch 117/49 47 R 1192 113 particles of the coating material dispersedtherein, the 117 54 120 201 213 47 A, 3; 29 3 10; particles beinginsoluble in the chlorofluoro ethane. 33 /303; 42 91 101 30 427 101 277The suspension is kept at a temperature higher than 299 331 375 430 thefreezing point of chlorofluoro ethane, and the article is immersed insaid suspension so as to form a fro- [56] R f r Ci zen layer of thesuspension on the surface of the arti- UNITED STATES PATENTS cle byfreezing of the chlorofluoro ethane. The article is taken out of thesuspension and the chlorofluoro ethane contained in the frozen layer isremoved by 2:427:417 9/1947 Prickettfi' /8 UX heating the art1cle at atemperature higher than the 2,976,188 3/1961 Kohl 7/8 X boiling point ofthe chlorofluoro ethane to leave 21 3,167,451 1/1965 Tierman 117/47 Rlayer of PertieleS Oh the article The article is then 3,200,471 8/1965Johnson et al 29/613 x ther heated so that the Particles remaining onthe 3,584,379 6/1971 Loose 29/610 face of the article form a layer ofthe coating material 3,722,077 3/1973 Armstrong 117/49 X on the article,3,728,144 4/1973 Van Poucke 117/1 19.2 X 3,736,179 5/1973 Gier et a1117/113 X 8 Claims, 7 Drawing Figures IIIIIIIIII/IIIj/IIIIIII'lIIII'III/III 11 j a 1 E I I 4 I z 1 I z j 0 o! 9 I r 9 'l a I u I 7 O og a 5 60 9' i x 11 s f 0 l US. Patent' Oct.21, 1975 Sheet 1 of33,914,466

0 0 ,0 e no u a v a vi a FIG] FIGZ

U.S. Patent Oct. 21, 1975 Sheet 2 of3 3,914,466

TEMP OF SUSPENSION: 27C 2 Q SIZE OF ARTICLE: 8 x 90(mm) CONCENTRATION:4OWc./o

(EPOXY RESI N) THICKNESS (mm) O I I I I I I -30 20 I O O IO 20 3OTEMPERATURE OF ARTICLE (C) U.S. Patent Oct. 21, 1975 Shcet3 0f33,914,466

FIG.4b

FIG.4d

METHOD FOR COATING AN ARTICLE BACKGROUND OF THE INVENTION This inventionrelates to a method for coating an article, and more especially to amethod of cool dip coating of an article suitable for mass-production.

There have been known various methods of coating articles with a resincoating or a glass coating. Practically, for the resin coating, the mostpopular method is one in which a vehicle including coating resinmaterial is applied to an article by spraying or dipping, and the thusapplied coating is cured after being dried. Another method is one inwhich a powdered coating resin is adhered to a heated article and iscured. For the glass coating, the conventional method is brush coatingor dipping. For both the resin coating and glass coating, there existproblems in that the coating applied according to the conventionalmethods has an irregular thickness from portion to portion over eachbody coated and has a rather small thickness. In addition, in case ofcoating electronic components, it is difficult in the conventionalmethods to prevent contamination of a portion of the lead wire of thecomponent to be soldered to an electric circuit.

OBJECTS AND BRIEF DESCRIPTION OF THE INVENTION It is an object of thisinvention to provide a method for coating articles with a thick coatingof resin or glass having a uniform thickness.

Another object of this invention is to provide a method for coating witha coating of resin or glass having no pin-holes and bubbles therein.

A further object of this invention is to provide a method for coatingarticles which is particularly effective for mass-production.

A further object of this invention is to provide a method for coatingelectronic components having lead wires attached thereto in which thelead wires are not contaminated by the coating material.

These objects are achieved by a method for coating an article withcoating particles comprising; cooling said article to a temperaturelower than the freezing point of chlorofluoro ethane which is anon-solvent for said coating particles, said chlorofluoro ethane beingthe suspending medium for a suspension with said coating particles ofsaid resin dispersed therein; immersing said article in said suspensionso as to form a layer of said suspension on the surface of said articleby freezing of said chlorofluoro ethane, said suspension being kept at atemperature higher than the freezing point of chlorofluoro ethane;taking said article out of said suspension; removing chlorofluoroethanecontained in said frozen layer by heating said article at a temperaturehigher than the boiling point of chlorofluoro ethane; and forming alayer of said resin of the remained particles on the surface of saidarticle by heating.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, and thefeatures of the invention will be apparent from a consideration of thefollowing detailed description taken together with the accompanyingdrawings, wherein:

FIGS. 1 and 2 are schematic views of an apparatus for carrying out thecoating method according to the present invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT According to theinvention, particles of coating material such as resin or glass to becoated are dispersed in a suspending medium which is a non-solvent forthese particles, and a suspension of the coating particles is formed. Asthe suspension is kept at a temperature higher than the freezing pointof the non-solvent suspending medium, it is in a fluid state. Further,the viscosity of the suspension is set so as to be suitable forimmersing the article to be coated in the suspension by controlling theconcentration of the particles of resin dispersed therein. For the caseof the resin coating, a preferable concentration of the particles isnearly 10 to 50 weight with respect to the non-solvent suspendingmedium. At a concentration of more than 50 weight the fluidity of thesuspension is decreased undesirably for immersing thearticle in thesuspension. For the glass coating, a preferable concentration is higherthan that for the resin coating because the specific gravity of theglass particles is higher than that of the resin particles.

The article to be coated is cooled to a temperature lower than thefreezing point of the non-solvent suspending medium and immersed in thesuspension. Then, due to freezing of the non-solvent, a frozen layer ofthe suspension is formed on the surface of the article. This frozenlayer is a mixture of the non-solvent suspending medium and the coatingparticles. If the article is left in the suspension having thetemperature higher than a freezing point of the non-solvent suspendingmedium, the formed layer will be melted in the suspension. Therefore,the article on the surface of which the frozen layer is formed is takenout of the suspension, and at once the article is heated so as toevaporate the non-solvent suspending medium and to form a resultantlayer consisting of only the coating particles. Then, by further heatingthe coating particles are cured and there is formed a uniform layer onthe article.

The coating method described above is useful for mass-production becauseof its simplicity, and the fonned layer is characterized by having arather large thickness and no pin-holes. Further, because of the coolingmethod, it is convenient to coat the article such as a film capacitorfor which heating is undesirable so that coating thereof is difficult bythe conventional method. Further, according to this method, an articleof any shape such as a tubular article can be easily coated. Somearticles having a complex shape are difficult to be coat theconventional methods such as spraying.

An operable material which can be used as the nonsolvent suspendingmedium for the resin particles includes a chlorofluoro ethane systemhaving a preferable freezing point near room temperature. When thefreezing point is too low, there are the problems in that it isdifficult and expensive to cool the article to be coated to atemperature lower than that freezing point. Further, as the article isapt to be wet due to the water content of the air, pin-holes are causedin the formed layer. On the other hand, when the freezing point of thenon-solvent suspending medium is too high, there is caused loss of thenon-solvent due to heating of the suspension. Further, if the boilingpoint of the non-solvent becomes too high, the resin particles aremelted before the non-solvent is evaporated fully and so the formedlayer becomes uneven because it contains the nonsolvent componenttherein. In addition, increasing the temperature of the suspension isundesirable because it decreases the pot life of the coating particles.Although there are various kinds of chlorofluoro ethanes, from the pointof practical working operation for cooling the article and evaporatingthe non-solvent, the preferrable ones are CCl FCCl F (designated by theinternational code 112), CCI CCIF (1 12a) and CCl FCClF (1 13a) whichhave freezing points of 23.5C, 406C and 14C, respectively and have theboiling points of 92.8C, 91.5 C and 45.7C, respectively. The temperatureof the suspension is kept slightly higher than freezing point of thenon-solvent suspending medium. When it is too high, the cooled articleimmersed therein is heated too quickly and the frozen layer of thesuspension is not formed.

If the suspension has a low concentration of the coating particles, whenthe non-solvent is evaporated from the frozen layer of the suspensionformed on the article during heating, there is sometimes caused slippingdown of the layer of the remaining particles. In this case, it iseffective to include a binder in the suspension. Then, the layer doesnot slip down but is transferred to the next curing process. In order toform a uniform layer, the binder should be soluble in the nonsolventsuspending medium for the resin particle, particles with which thearticle is being coated. For the case of a resin coating, materialsoperable as a binder include polystyrene and denatured silicon resin.The latter dissolves epoxy resin, which is preferably used as thecoating material for the method of the invention,

' well. The preferable concentration of the binder ranges 0.1 to 5.0weight Too much binder has an undesirable influence on the properties ofthe resin particles and causes uneveness of the resultant layer.

Now, there will be described in more detail embodiments of the inventionin the following examples.

EXAMPLE 1 Disk type resistors were coated with epoxy resin as describedhereinafter referring to FIGS. 1 and 2. In FIG. 1, the disk typeresistors designated by the reference numeral 1 were cooled to atemperature of nearly 5C in a cooling room 2. Dried air was continuouslyfed into the cooling room 2 and an immersing room 3 from an inlet 4. Thecooled resistors were transferred to the immersing room 3 past a heatshielding wall 5, and immersed in a suspension 6 contained in animmersing tank 9.

The suspension 6 was formed by particles of epoxy resin having thehereinafter described composition as the coating material and a mixtureof 90 weight parts of 1,2-difluoro, l,1,2,2- tetrachloro ethane (CClFCCl F) and 10 weight parts of 2,2-difluoro 1,l,1,2-tetrachloro ethane(CCl CClF which was a non-solvent for the particles. Such a mixture isavalable on the market under the trade name Daiflon S (made byDaikin-kogyo Co., Japan), which has a freezing point of 26C and aboiling point of 91 to 93C. The composition of the epoxy resin is asfollows:

principal component: BIS phenol-A type epoxy resin,

Epikote 1007 (Shell Chem. Co. USA.) g

hardener: aromatic amine,

4,4 Diamino-Diphenyl Sulfone 3.5g filler: SiO, 25g lubricant: Stearicacid 1.0g pigment: re o, l 1 g The composition has a melting point of100 to 1 19C. The concentration of the particles of epoxy resin in thesuspension was 10 to 50 weight The temperature of the suspension wascontinuously kept nearly at 30C by means of a heater 10 and a cooler 11.Further, the suspension was loosely stirred by a stirrer 12 so as tomake the concentration of the particles in the suspension uniform. Whenthe resistors were immersed in the suspension 6, the stirring wasstopped. A frozen layer 7 was thus formed on each resistor.

After the resistors were immersed in the suspension for 5 seconds, theresistors were taken out therefrom. There was a frozen layer 13 of thesuspension, i.e., the mixture of the particles of epoxy resin and thenonsolvent suspending medium Daiflon 5;, on the surface of eachresistor. The resistors 1 taken out of the suspension were instantlytransferred to the next step of the process. That is, the non-solventwas evaporated by heating the resistors in a drying room 14 shown inFIG. 2. Then, there was formed a layer 15 consisting of only theparticles of epoxy resin.

The layer 15 may slip down if some vibration is applied to the resistor.Also, with a low concentration of the particles of epoxy resin in thesuspension, there may be caused a similar problem. The slipping down ofthe layer 15 can be prevented by adding polystyrene in a concentrationof 100 ppm to the suspension as a binder. Denatured silicon resin wasalso effective for preventing the slipping down of the layer 15.

The dried layer 15 was further heated at C, the curing temperature forthe epoxy resin, for 20 minutes, and then there was formed a cured layer16. The thickness of the resultant layer was 1.0 to 1.2 mm.

The transferring of the resistors into and out of the rooms 2, 3 and 14were carried out continuously by providing shutter mechanism. The vaporof the nonsolvent in the drying room 14 was absorbed by a vacuum pump 17and condensed by a cooler 18. The condensed vapor can be collected in acontainer 19. This is desirable for reducing the coating cost.

Usually, the thickness of the formed layer increases in accordance withan increase of temperature difference between the article to be coatedand the suspension. FIG. 3 shows such a relation between the temperatureof the article and the thickness of the resultant layer for theconditions indicated in the figure.

EXAMPLE 2 A suspension similar to that of Example 1 was used. Theconcentration of the particles of epoxy resin was 35 to 45 weight andthe temperature of the suspension was kept at 27 to 32C. Threeresistors, of the axial of electronic component having two lead wiresextending longitudinally from both ends, one 8 mm in diameter and 40 mmin length, 8 mm in diameter and 20 mm in length, and one 1.5 mm indiameter and 8 mm in length, were cooled to a temperature of 9 to 15C,and immersed in the suspension 41 for 5 to 10 seconds to a depth suchthat 1.5 mm of one lead wire 44 above the upper end of the resistor body42 was covered, as shown in FIG. 4(a). Then, the frozen layer 43 of thesuspension was formed, as shown in FIG. 4(a) and FIG. 4(b), on thesurface of the resistor body 42, the other lead wire 44 and the part ofthe lead wire 44, which were immersed in the suspension 41.

After the resistors were taken out of the suspension, a cutter 45 waspressed into the frozen layer formed on the lead wire 44 from ahorizontal direction A, as shown in FIG. 4(0), so as to cut that layer,and then the cutter 45 was moved as while being held in the cuttingposition downwardly in the direction B sliding along the lead wire 44'.By this operation, the frozen layer 46 formed on the lead wire 44 waseasily separated therefrom.

This process of pressing and moving the cutter was carried out while theformed frozen layer 43 was kept as it was. Even by this process, thelayer 43 formed on the resistor body was not deformed. It was notnecessary to cut around the complete circumference of the lead wire 44,and even by cutting only a part of the layer 46 it could be easilyseparated. Then, there remained only the desired portion the layer, i.e.on the resistor body and on a part of the lead wires.

Then, similarly to Example 1, the resistors were put in the drier at120C, wherein at first the non-solvent was evaporated and the surface ofthe particles of epoxy resin were partially melted, by which meansslipping down of the layer due to heating could be prevented. Inaccordance with increase of temperature, the particles of epoxy resinmelted and there was formed a uniform layer 47 as shown in FIG. 4(d).The thickness of the resultant layer was 0.6 to 1.0 mm.

EXAMPLE 3 A suspension was made with the same non-solvent suspendingmedium as that of the example 1 and 30 weight of particles of nylon 12,and 2 weight of polystylene were dissolved in the suspension as abinder. The same resistor as that of the example 2 was immersed in thesuspension, and the frozen layer of the suspension was formed similarly.After separating the layer on the lead wire similarly to example 2, theremaining layer was cured by heating the resistor at 200C. Then, therewas formed a uniform layer of nylon 12.

EXAMPLE 4 33 weight of particles of polyvinyl chloride were dispersed inthe same non-solvent suspending medium as that of example 1, and acooled iron plate was immersed in the resultant suspension. The frozenlayer of the suspension formed on the surface of the iron plate wascured at 120C, and there was provided an iron plate coated a uniformlayer of polyvinyl chloride.

EXAMPLE 5 Wirewound resistors were coated with glass of having a lowmelting point by using suspension system having the followingcomposition:

glass powder 100g binder; ethylcellulose 2.15g non-solvent suspendingmedium; 193.2g

The glass powder consisted of 88 weight of PbO and 12 weight of B 0 andhad a 1.011 average grain size. The suspension was kept at 27C, and thewirewound resistors cooled at -l 2C were immersed in the suspension, sothat the frozen layer of the suspension was formed on the surface of theresistor. After taking the resistors out of the suspension, at first thenon-solvent was evaporated, and then the resistors were kept at nearly300C for 30 minutes so that the binder was burned away completely. Afterthat, the resistor was further heated at 350C for 10 minutes to melt theglass powder completely. Then, the resistor was cooled to roomtemperature at a rate of 10C/minute, and a uniform glass layer having nopin-holes and having a thickness of 0.8 mm was formed on the surface ofthe wirewound resistor.

What is claimed is:

l. A method for coating an article with a layer of coating materialcomprising:

cooling said article to a temperature lower than the freezing point of achlorofluoro ethane; providing a suspension of said chlorofluoro ethaneas a suspending medium with coating particles of the coating materialdispersed therein, the particles being insoluble in the chlorofluoroethane;

keeping said suspension at a temperature higher than the freezing pointof chlorofluoro ethane;

immersing said article in said suspension so as to form a frozen layerof said suspension on the surface of said article by freezing of saidchlorofluoro ethane;

taking said article out of said suspension;

removing the chlorofluoro ethane contained in said frozen layer byheating said article at a temperature higher than the boiling point ofsaid chlorofluoro ethane to leave a layer of particles on the article;and

heating the article and the particles remaining on the surface of saidarticle to form a layer of the coating material on the article.

2. A method as claimed in claim 1, wherein said chlorofluoro ethane isselected from the group consisting of CCl FCCl F, CCl CClF and CCI FCClF3. A method as claimed in claim 1, wherein said coating particles areparticles of resin.

4. A method as claimed in claim 3, wherein said particles of resin aredispersed in said suspension in a concentration of 10 to 50 weightrelative to said chlorofluoro ethane.

5. A method as claimed in claim 3, wherein said suspension contains abinder which is soluble in chlorofluoro ethane in a concentration of 0.1to 5.0 weight said binder being selected from the group consisting ofpolystyrene and denatured silicone resin.

6. A method as claimed in claim 1, wherein said coating particles areglass particles.

7. A method as claimed in claim 1, wherein said article is an electroniccomponent.

8. A method as claimed in claim 7, wherein said electronic component isan axial type component having two lead wires extending longitudinallyfrom both ends thereof, one of said two lead wires and the whole body ofsaid electronic component being immersed in said suspension, includingthe step of cutting off the layer of said suspension formed on thesurface of said immersed lead wire, after the step of taking saidcomponent out of said suspension.

1. A METHOD FOR COATING AN ARTICLE WITH A LAYER OF COATING MATERIALCOMPRISING: COOLING SAID ARTICLE TO A TEMPERATURE LOWER THAN THEFREEZING POINT OF A CHLOROFLUORO ETHANE: PROVIDING A SUSPENSION OF SAIDCHLOROFLUORO ETHANE AS A SUSPENDING MEDIUM WITH COATING PARTICLES OF THECOATING MATERIAL DISPERSED THEREIN, THE PARTICLES BEING INSOLUBLE IN THECHLOROFLUORO ETHANE: KEEPING SAID SUSPENSION AT A TEMPERATURE HIGHERTHAN THE FREEZING POINT OF CHLOROFLUORO ETHANE: IMMERSING SAID ARTICLEIN SAID SUSPENSION SO AS TO FORM A FROZEN LAYER OF SAID SUSPENSION ONTHE SURFACE OF SAID ARTICLE BY FREEZING OF SAID CHLOROFLUORO ETHANE:TAKING SAID ARTICLE OUT OF SAID SUSPENSION: REMOVING THE CHLOROFLUOROETHANE CONTAINED IN SAID FROZEN LAYER BY HEATING SAID ARTICLE AT ATEMPERATURE HIGHER THEN THE BOILING POINT OF SAID CHLOROFLUORO ETHANE TOLEAVE A LAYER OF PARTICLES ON THE ARTICLE, AND HEATING THE ARTICLE ANDTHE PARTICLES REMAINING ON THE SURFACE OF SAID ARTICLE TO FORM A LAYEROF THE COATING MATERIAL ON THE ARTICLE.
 2. A method as claimed in claim1, wherein said chlorofluoro ethane is selected from the groupconsisting of CCl2FCCl2F, CCl3CClF2 and CCl2FCClF2.
 3. A method asclaimed in claim 1, wherein said coating particles are particles ofresin.
 4. A method as claimed in claim 3, wherein said particles ofresin are dispersed in said suspension in a concentration of 10 to 50weight % relative to said chlorofluoro ethane.
 5. A method as claimed inclaim 3, wherein said suspension contains a binder which is soluble inchlorofluoro ethane in a concentration of 0.1 to 5.0 weight %, saidbinder being selected from the group consisting of polystyrene anddenatured silicone resin.
 6. A method as claimed in claim 1, whereinsaid coating particles are glass particles.
 7. A method as claimed inclaim 1, wherein said article is an electronic component.
 8. A method asclaimed in claim 7, wherein said electronic component is an axial typecomponent having two lead wires extending longitudinally from both endsthereof, one of said two lead wires and the whole body of saidelectronic component being immersed in said suspension, including thestep of cutting off the layer of said suspension formed on the surfaceof said immersed lead wire, after the step of taking said component outof said suspension.